Poster: Root biology

Abs # 702: Expression of β-glucosidase and its role in activating zeatin-O-glycoside during cold-stress recovery in Zea mays root tip.

Presenter:	Silva, Keri E, kereeze@sbcglobal.net
Authors	Silva, Keri E (A)   Allen, Josephine  (A)   Zavala, MariaElena  (A)
Affiliations:	(A): California State University, Northridge

β-Glucosidases are enzymes that catalyze the cleavage of β-linked sugars from glycosides. These enzymes are important in plants for development and growth, lignin biosynthesis and defense mechanisms against insect pests and pathogens. A previous study showed that β-glucosidase encoded by the Zm-p60.1 gene that was transiently expressed was capable of hydrolyzing exogenous inactive cytokinin, zeatin-O-glycoside, to zeatin, the active form, enabling the tobacco protoplasts to undergo cell division (Brzobohaty et. al. 1993). The role of β-glucosidase in zeatin metabolism was studied in Zea mays root tips during cold-stress and subsequent recovery. Three-day old Zea mays seedlings were cold-stressed at 4^oC for four days and returned to room temperature for a cold-stress recovery period. β-Glucosidase activity and mRNA were tested. A dramatic increase in β-glucosidase activity was observed following a 24-hour recovery period. This corresponds to a decrease of zeatin-O-glycoside levels, an increase in zeatin levels, and a resumption of growth. Northern analysis of control, cold-stress and cold-stress recovered root tip RNA suggests that the expression pattern of Zm-p60.1 in the cold-stress and recovered Zea mays do not differ significantly from the control. These results support the hypothesis that β-glucosidase gene expression in Zea mays root-tips is continuous. The dramatic increase in β-glucosidase enzyme activity in the 24-hour recovery period may be due to a change in its activation or localization. Supported by NIH T32 GM08395, NIH R25 GM62019 and NSF HRD 0003108.